In a lens barrel of, for instance, a camera, a cylinder (hereafter referred to as a cam cylinder) with a cam groove formed at the inner circumferential surface thereof is rotatably disposed so as to rotate around the optical axis. Operations such as zooming are executed by engaging or fitting a cam follower projecting from a lens unit in the cam groove and driving the lens unit forward/backward along the optical axis as the cam cylinder rotates. The extent of lens displacement per unit of rotational angle by which the cam cylinder rotates is determined in correspondence to the gradient of the cam groove and the relationship between the extent of lens displacement and the unit of rotational angle remains constant as long as the gradient of the cam groove is uniform, i.e., as long as the cam groove forms a single straight line in a plan development of the cam cylinder. There is a structure that allows the extent of lens displacement relative to the unit of rotational angle by which the cam cylinder rotates to be variable by altering the gradient of the cam groove (see patent reference literature 1). Patent reference literature 1 also discloses a method for forming such a cam groove at the inner circumferential surface of a cam cylinder by using a plurality of split molds.
Patent reference literature 1: Japanese Laid Open Patent Publication No. 2001-221941